1. Field of the Invention:
The present invention relates to a power supply device of comparatively large capacity that includes a plurality of series-connected-battery blocks which are connected in parallel and in each of which two or more secondary cells capable of charging and discharging are connected in series.
2. Description of the Related Art:
There has been proposed a power supply device of comparatively large capacity that includes a plurality of series-connected-battery blocks which are connected in parallel and in each of which two or more secondary cells capable of charging and discharging are connected in series. In such power supply device, when connecting a plurality of series-connected-battery blocks in parallel, in each of which two or more secondary cells capable of charging and discharging are connected in series, a rush current flows into a series-connected-battery block of a low potential difference from a series-connected-battery block of a high potential difference.
Since the rush current is limited only by an internal impedance of the series-connected-battery blocks, there is a possibility of damaging the series-connected-battery block of a low potential difference.
FIG. 1 shows related art in which a plurality of series-connected-battery blocks are connected in parallel through diodes. In FIG. 1, each of reference numerals 1, 2 and 3 denotes a series-connected-battery block in which two or more, for example four, secondary cells capable of charging and discharging, lithium-ion secondary cells for example, are connected in series.
A positive electrode of the series-connected-battery block 1 is connected to a cathode of a diode 1a and is connected to an anode of a diode 1b; a positive electrode of the series-connected-battery block 2 is connected to a cathode of a diode 2a and is connected to an anode of a diode 2b; and a positive electrode of a series-connected-battery block 3 is connected to a cathode of a diode 3a and is connected to an anode of a diode 3b. 
Each anode of the diodes 1a, 2a and 3a is connected to a charge positive terminal 4 of the power supply device, respectively. Specifically, when each anode of the diodes 1a, 2a and 3a is connected in parallel to the charge positive terminal 4, the diodes 1a, 2a and 3a function as those for preventing reverse current, and so no rush current flows when connected in parallel and each of the series-connected-battery blocks 1, 2 and 3 is prevented from being damaged.
Further, each cathode of the diodes 1b, 2b and 3b is connected to a discharge positive terminal 5 of the power supply device, respectively. Specifically, when each cathode of the diodes 1b, 2b and 3b is connected in parallel to the discharge positive terminal 5, the diodes 1b, 2b and 3b function as those for preventing reverse current, and so no rush current flows when connected in parallel and each of the series-connected-battery blocks 1, 2 and 3 is prevented from being damaged.
Further, each negative electrode of the series-connected-battery blocks 1, 2 and 3 is connected to a negative terminal 6 of the power supply device.
In such power supply device of the past as shown in FIG. 1, when charging, a charge current flows into the series-connected-battery blocks 1, 2 and 3 through the diodes 1a, 2a and 3a to charge; and when discharging, the series-connected-battery blocks 1, 2 and 3 are connected to a load through the diodes 1b, 2b and 3b to discharge.
Further, in the related art of FIG. 1, when the series-connected-battery blocks 1, 2 and 3 with potential differences are connected in parallel, current does not flow among the series-connected-battery blocks 1, 2 and 3 due to the diodes 1a, 2a, 3a, and 1b, 2b, 3b. Therefore, even if the series-connected-battery blocks 1, 2 and 3 with potential differences are connected in parallel, each of series-connected-battery blocks 1, 2 and 3 is prevented from being damaged, because no rush current flows.
Japanese Published Patent Application No. H10-304586 discloses a charging device for secondary batteries, including a plurality of series-circuits of the secondary batteries, which are connected in parallel and in each of which two or more secondary cells are connected in series. In this patent literature, there is no description of preventing the rush current when respective series-connected secondary batteries are connected in parallel.